In automatic hook-type couplers, it is desirable to have a gathering range which is sufficiently large to permit engagement and alignment of coupler heads from initial conditions of misalignment which are largely a function of operating circumstances. In certain transit and other applications, it has become necessary to enlarge this range or zone beyond that which is currently available. However, this must be done without significantly increasing the outer dimensions of the coupler head.
Presently, the gathering range is determined by hook and pocket configurations and, in a 2.5 inch hook coupler, the gathering zone, viewed in a vertical plane, is a non-symmetrical region which is about 8.25 inches wide and about 6 inches high at the largest point. This is not sufficient to satisfy present needs.
Examples of couplers of the general type to which the invention relates can be found in U.S. Pat. Nos. 3,405,811, Cope; 3,655,066, Metzger; and 4,073,385, Reed. Metzger is of particular interest as an example of the prior art as well as for its discussion of the general problem.
A hook-type coupler of this general type includes a head with a generally flat front face and an opening through the face which forms a pocket. A hook protrudes through the pocket, offset to one side, and is designed to engage a similar hook in a mating coupler head. The face also has at least one protruding alignment pin, generally with a tapered end, and an opening for receiving a similar pin in the other head. Various surfaces of the pocket opening, hook alignment pin, and pin socket are slanted in various ways so that they can guide each other toward alignmcnt.
However, there are distinct limitations on the sizes of such surfaces and the dimensions of the protruding components, placing upper limits on the gathering range.
An additional constraint is imposed by the presence of electric coupler heads, particularly side mounted electric coupler heads, which have electrical contact sets to be engaged as the mechanical coupler parts are joined. It has been found that previously used mechanical couplers sometimes approach each other in such a way that the contact sets are misaligned and are seriously damaged. This is believed to occur because the flat faces of the mechanical heads are not always parallel with each other during the last stages of the coupling operation.